14
It is 11 which is also a prime number
It is 12 because 3*6*12 = 216.
3, 6, 9, 12, and 13
(12/13)x = 20x = 20 / (12/13) = (20 x 13) / 12 = 21 and 2/3
14
This missing number is 5
It is 11 which is also a prime number
13/16 3+9=12 4+8=12 12 is divisible by 3 39/3=13 48/3=16 13/16 can not both be divided by the same number (13 is a prime number)
The missing number is 1321!!! Simple Fibonacci row! 0+1=1 1+1=2 1+2=3 2+3=5 3+5=8 5+8=13 8+13=21 13+21=34 ......
It is 12 because 3*6*12 = 216.
6
1 2 3 4 5 6 7 8 9 10 11 12 13. Could not be simpler!
3, 6, 9, 12, and 13
(12/13)x = 20x = 20 / (12/13) = (20 x 13) / 12 = 21 and 2/3
13 is one such number.
3 x 4 = 12... 1 + 12 = 13... 13 x 2= 26